Tunable Carrier Concentration of NaF‐Treated CIGS Solar Cells Using Heat–Light Soaking and Subsequent Heating

Physica Rapid Research Ltrs

Yashiro

Lin

et al. 2020

Self Cite

Metastable behavior of cesium fluoride (CsF)‐treated Cu(In1–x,Gax)Se2 (CIGS) solar cells is investigated under heat‐light soaking (HLS) and heat‐soaking (HS) treatments. HLS increases open‐circuit voltage, fill factor, efficiency, and net carrier concentration and decreases short‐circuit current density, whereas heat‐soaking treatment acts oppositely. The performance of a CsF postdeposition treatment to CIGS thin film in selenium vapor, and closer to stoichiometry copper content, did not mitigate the open‐circuit voltage improvement after HLS. These results argue the traditional concept of the VSe–VCu divacancy complex for the total beneficial effect of HLS in alkali‐treated CIGS solar cells. The metastable behavior observed in the CsF‐treated devices due to the HLS and HS treatments is explained by the specific behavior of alkali‐containing new compounds at the surface and/or the migration of alkali metals at the surface and bulk regions.

supporting

confidence: 84%

mentioning

confidence: 91%

mentioning

confidence: 99%

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confidence: 99%

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Metastable Behavior on Cesium Fluoride‐Treated Cu(In_1–x,Ga_x)Se₂ Solar Cells

Physica Rapid Research Ltrs

Yashiro

Lin

et al. 2020

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“…The HLS had a beneficial effect on the KF‐treated CIGS solar cells by improving the open‐circuit voltage ( V OC ) and fill factor (FF) . A similar effect was observed for sodium fluoride (NaF)‐treated and cesium fluoride (CsF)‐treated CIGS solar cells . The improved V OC was attributed to a significantly increased net carrier concentration ( N CV ), rather than to change in the atomic concentrations of Cd, S, and O in the chemical bath deposition (CBD) cadmium sulfide (CdS) buffer layer.…”

Section: Introductionmentioning

confidence: 71%

Effect of heat‐bias soaking on cesium fluoride‐treated CIGS thin film solar cells

Progress in Photovoltaics

Matsuura

Sugiyama

et al. 2018

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The combined effect of heating and forward bias voltage, that is, heat‐bias soaking (HBS) on cesium fluoride (CsF)‐free and CsF‐treated Cu(In1‐xGax)Se2 (CIGS) solar cells using chemical bath deposition‐cadmium sulfide (CBD‐CdS) buffer layer was investigated with varying the heating temperature, bias voltage, and biasing time. Heat bias soaking followed by heat soaking (HS) (ie, HBS/HS) treatments improved the open‐circuit voltage (VOC) and conversion efficiency for the CsF‐treated CIGS solar cell, whereas such a beneficial effect was not observed for CsF‐free CIGS solar cells. Capacitance‐voltage measurement confirmed the significantly increased carrier concentration (NCV) after HBS for the CsF‐CIGS solar cell, which is one of the possible reasons for the increased VOC. Because of the extremely high NCV, the short‐circuit current density (JSC) decreased owing to the narrower depletion width. However, the high NCV could be tuned to an appropriate value via a subsequent moderate heating procedure without biasing. As a result, the JSC loss was reduced, thereby improving the cell efficiency. These results open a new route to improve the efficiency of alkali‐treated CIGS solar cells.

Impact of heat‐light soaking and heat‐bias soaking on NaF‐treated CIGS thin film solar cells

Matsuura

Progress in Photovoltaics

Lin

et al. 2019

Self Cite

The effects of heat-light soaking (HLS) and heat-bias soaking (HBS) were investigated on NaF-treated Cu (In,Ga)Se 2 (CIGS) solar cells. The HLS improved the cell efficiency with increased open-circuit voltage (V OC ) for NaF-treated CIGS solar cells, whereas the short-circuit current density (J SC ) slightly decreased. The reduced J SC was caused by the significantly high carrier concentration due to the HLS, leading to a fairly narrow space charge region. However, the reduced J SC could be successfully recovered by the subsequent moderate heat soaking (HS) in the dark, thereby improving cell efficiency. On the other hand, no beneficial effect was observed for NaF-free solar cells. Secondary ion mass spectrometry (SIMS) measurements revealed that the Na and K ions increased especially near the CIGS surface region after the HLS process. This result suggests that these ions were shifted by the photo-induced electric field. The thermally and electrically activated alkali ions may eliminate the donorlike defects in CIGS absorber, resulting in an increased acceptor concentration. Furthermore, we found that an external forward bias without light irradiation (HBS) resulted in the same effect as HLS. Based on these results, a possible mechanism of HLS and HBS effects was proposed on NaF-treated CIGS solar cells.